Synthesis and characterization of some calamitic liquid crystals consisting of cholesterol, rod-like imine and biphenyl-4-carboxylate components

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dc.contributor.authorHa, Sie Tiong
dc.date.accessioned2014-11-03T02:34:48Z
dc.date.available2014-11-03T02:34:48Z
dc.date.issued2006
dc.descriptionPhDen_US
dc.description.abstractSeven series of calamitic liquid crystals were successfully synthesized and characterized. These liquid crystals are categorized into three different types according to their core structure; either a cholesterol, rod-like aromatic imine or biphenyl-4-carboxylate component. The synthesis of these compounds basically involved alkylation, esterification and condensation reactions. The structures of the synthesized compounds were established by CHN microanalysis along with several spectroscopic techniques such as FTIR, 1Dand 2D-NMR. Whilst the phase transitions and liquid crystal textures were observed by using polarized optical microscope, the respective transition temperatures and associated enthalpies were determined by using DSC analysis. The first and second series which consist of seven homologues each, include cholesteryl 4-n-alkoxybenzoates (nOACh) and cholesteryl 4-(4-nalkoxyphenyl) benzoates (nOABCh). Various alkoxy groups consisting of even numbered carbons ranging from six to eighteen have been adopted throughout this study. The various NMR techniques which were employed revealed that the O=C-O bridging the phenyl group and the cholesteryl fragment was bent and led to the cholesteryl fragment to fold up. This unique conformation has been observed for the first time in cholesteryl esters. Both of the series showed that the lower members have a higher tendency to exhibit chiral nematic (N*) phase whereas the higher members showed a greater tendency to display the smectic A (SmA) phase. The third, fourth, fifth and sixth series each consists of a rod-like aromatic imine component. The third series is further divided into three sub-series; 2-hydroxy-4-methoxybenzylidene-4’-n-alkanoyloxyanilines (nSBA), 2-hydroxy-3-methoxybenzylidene-4’-n-alkanoy-loxyanilines (nSBB) and 3-methoxy-4-n-alkanoyloxybenzylidene-4’-n-alkanoy-loxyanilines (nSBC). Each of them comprised four members which differed in the alkanoyloxy chain length. Whilst the nSBA homologues exhibited the enantiotropic nematic or SmA phase, the nSBC homologues displayed the monotropic smectic C (SmC) phase. However, the nSBB homologues did not exhibit any mesophase. The fourth, fifth and sixth series encompassed 2-hydroxy-4-nhexadecanoyloxybenzylidene- 4’-substituted-anilines (16OHA-R), N-[4-(4-nhexadecanoyloxybenzoyloxy) benzylidene]-4-substituted-anilines (16AB-R) and N-[4-(4-n-hexadecanoyloxybenzoyloxy)-2-hydroxybenzylidene]-4-substitutedanilines (16OHAB-R), in which R is H, F, Cl, Br, OCH3, CH3, C2H5, CN, OH, SH or NO2. While compounds 16OHA-R with the substituents R = H, F, Cl, Br, OCH3, CN, OH and NO2 exhibited SmA phase, those with the substituents R = CH3 and C2H5 showed monotropic SmC phase and finally the compound with R = SH displayed monotropic nematic phase. Compounds 16AB-R and 16OHABR (where R = H, OCH3, CH3, C2H5, OH and NO2) showed evidence of nematic phase while compounds 16AB-R and 16OHAB-R (where R = F, Cl, Br and CN) exhibited SmA phase. Compound 16OHAB-SH exhibited nematic phase whereas compound 16AB-SH did not show any mesophase. The 16AB-R and 16OHAB-R molecules have a higher mesophase stability compared to the 16OHA-R molecules owing to their higher molecular length. The mesomorphic properties of these compounds were also influenced by the intermolecular and intramolecular interactions owing to the presence of the ortho-hydroxyl group. The seventh series with a biphenyl-4-carboxylate core consists of four (S)-2- methylbutyl 4’-(4”-n-alkanoyloxybenzoyloxy)biphenyl-4-carboxylate (S-MBOOCn) homologues. All the S-MB-OOCn homologues exhibited the chiral smectic C (SmC*) and SmA phases.en_US
dc.identifier.urihttp://hdl.handle.net/123456789/316
dc.language.isoenen_US
dc.subjectChemical scienceen_US
dc.subjectCalamitic liquid crystalsen_US
dc.subjectRod-like imineen_US
dc.subjectBiphenyl-4-carboxylateen_US
dc.titleSynthesis and characterization of some calamitic liquid crystals consisting of cholesterol, rod-like imine and biphenyl-4-carboxylate componentsen_US
dc.typeThesisen_US
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